mastodon: tighten resources, robust exec tasks, and env defaults

- resources: per-service cpus/mem/pids for mastodon/streaming/sidekiq/redis/db
- compose: rename service key to "mastodon" (was: web), set service_name blocks
- tasks(01_setup): run rails db:migrate via docker exec (non-tty, login shell)
- tasks(02_administrator): healthchecks for 'mastodon', sed with absolute path,
  tootctl as user 'mastodon' (non-tty), optional re-health wait
- env.j2: add RAILS_ENV={{ ENVIRONMENT | default('production') }}
- resource.yml.j2: fix get_app_conf path (service_name default spacing)
- docs: remove outdated Installation/Administration files

Context: https://chatgpt.com/share/68d332a0-ae98-800f-b418-c0d0262eaa2e

roles/web-app-mastodon/tasks/01_setup.yml

@@ -1,7 +1,6 @@
 - name: "Execute migration for '{{ application_id }}'"
   command:
-    cmd: "docker-compose run --rm web bundle exec rails db:migrate"
-    chdir: "{{ docker_compose.directories.instance }}"  
+    cmd: "docker exec {{ MASTODON_CONTAINER }} bundle exec rails db:migrate"
 
 - name: "Include administrator routines for '{{ application_id }}'"
   include_tasks: 02_administrator.yml